add dis optical flow sample app

it takes a video file as input and shows colored optical flow.
Signed-off-by: Li Peng <peng.li@intel.com>

modules/optflow/samples/dis_opticalflow.cpp

+
+#include "opencv2/core/utility.hpp"
+#include "opencv2/highgui.hpp"
+#include "opencv2/imgproc.hpp"
+#include "opencv2/optflow.hpp"
+
+using namespace std;
+using namespace cv;
+using namespace optflow;
+
+static void help()
+{
+    printf("Usage: dis_optflow <video_file>\n");
+}
+
+int main(int argc, char **argv)
+{
+    VideoCapture cap;
+
+    if (argc < 2)
+    {
+        help();
+        exit(1);
+    }
+
+    cap.open(argv[1]);
+    if(!cap.isOpened())
+    {
+        printf("ERROR: Cannot open file %s\n", argv[1]);
+        return -1;
+    }
+
+    Mat prevgray, gray, rgb, frame;
+    Mat flow, flow_uv[2];
+    Mat mag, ang;
+    Mat hsv_split[3], hsv;
+    char ret;
+
+    namedWindow("flow", 1);
+    namedWindow("orig", 1);
+
+    Ptr<DenseOpticalFlow> algorithm = createOptFlow_DIS(DISOpticalFlow::PRESET_MEDIUM);
+
+    while(true)
+    {
+        cap >> frame;
+        if (frame.empty())
+            break;
+
+        cvtColor(frame, gray, COLOR_BGR2GRAY);
+
+        if (!prevgray.empty())
+        {
+            algorithm->calc(prevgray, gray, flow);
+            split(flow, flow_uv);
+            multiply(flow_uv[1], -1, flow_uv[1]);
+            cartToPolar(flow_uv[0], flow_uv[1], mag, ang, true);
+            normalize(mag, mag, 0, 1, NORM_MINMAX);
+            hsv_split[0] = ang;
+            hsv_split[1] = mag;
+            hsv_split[2] = Mat::ones(ang.size(), ang.type());
+            merge(hsv_split, 3, hsv);
+            cvtColor(hsv, rgb, COLOR_HSV2BGR);
+            imshow("flow", rgb);
+            imshow("orig", frame);
+        }
+
+        if ((ret = (char)waitKey(20)) > 0)
+            break;
+        std::swap(prevgray, gray);
+    }
+
+    return 0;
+}